The present invention relates to a reactive anthraquinone compound useful as a dye, and a lens, in particular, a contact lens, which is colored by the anthraquinone compound.
Most of the currently commercially available lenses are variously colored. Colored lenses have been required for and made with the purposes of improving optical performance and visibility and for their fashionable appearance.
Currently utilized methods for coloring contact lenses are classified into two kinds, i.e., (1) a method of copolymerizing a comonomer solution containing a common and conventional dye, and (2) a method of utilizing a vat dye comprising immersing a transparent lens prepared by the cutting and polishing method or the casting method into a vat dyeing bath so that a lueco dye (reduced compound) can sufficiently impregnate the lens and then immersing the lens into an oxidation bath to convert the leuco dye into a oxidated compound so that the dye is fixed.
In both of the methods mentioned above, dye is retained in the lens material by the absorptivity of the dye to the material or steric hindrance of the network of the lens material. In these cases, however, the dye is simply dispersed in the lens material and enclosed by the absorptivity of the dye to the material or steric hindrance of the network of the lens material. Therefore, with respect to O.sub.2 permeable hard contact lenses, which have a low glass transition point and are relatively soft at room temperature, or non-water-retaining soft contact lenses and water-retaining soft contact lenses, dissolution or bleeding of the dye is a serious problem.
To solve such a problem, a reactive dye having a monomer structure similar to that of monomers of lens materials has been proposed. See, for example, EP 0 396 376 A1. This patent document discloses a reactive dye represented by the following formula 3: ##STR3## wherein X represents an unsaturated polymerizable organic residue and P represents a C2-C12 organic divalent residue.
Such a reactive dye as mentioned above can form a copolymer with monomers of the lens material and hence can ameliorate the problem of the dissolution or bleeding out of the dye. However, if the dyes specifically disclosed in EP 0 396 376 A1 were used, they are likely to be hydrolyzed by a nucleophile, in particular water and the like, because their reactive double bonds derived from the starting monomers and the dye units are bonded through an ester bond or amide bond. As a result, secondary dissolution or bleeding of the dye units may occur.
In addition, some of these reactive dyes can hardly be copolymerized because of their poorly copolymerizable structures.
The dissolution of the dye units caused by hydrolysis and the dissolution of unreacted dyes because of their poor copolymerizability are extremely important factors degrading the safety of lenses. These dissolutions greatly depend on the conditions in which the lenses are used. However, the dye units, i.e., the anthraquinone compounds, are quite toxic and therefore the reactive dyes showing excellent hydrolysis resistance and good copolymerizability have been desired so that safer lenses can be provided.
Accordingly, one object of the present invention is to provide a novel reactive dye which shows excellent hydrolysis resistance and good copolymerizability with other material monomers as well as excellent dyeing ability and proper solubility in the material monomers.
A second object of the present invention is to provide a method for producing copolymers utilizing the reactive dye mentioned above and a lens such as a contact lens comprising a copolymer formed by utilizing the reactive dye mentioned above.